1. Field
The following disclosure relates to a terminal and method for switching between radio access technologies.
2. Discussion of the Background
A circuit switched fallback (CSFB) technique may be used to process a circuit switched call by switching from a long-term evolution (LTE) network to a 3rd generation (3G) network or to a 2nd generation (2G) network if the circuit switched call is requested while connecting to the LTE network, and reverting to the LTE network if the circuit switched call is terminated. The circuit switched call using the CSFB procedure (CSFB call) may be processed by enabling fallback from the LTE network to the 3G/2G network for switching between radio access technologies (RATs). This may involve a procedure of registering a location of a terminal in the 3G/2G network. The subsequent switching back to the LTE network may be executed based on LTE redirection information included in a 3G radio resource control (RRC) connection release message.
FIG. 1 is a diagram illustrating a process of transitioning to a long-term evolution (LTE) network using LTE redirection information after terminating a circuit switched fallback (CSFB) call. Referring to FIG. 1, a user equipment or mobile station (UE/MS) 101 supporting LTE communication protocols may request a CSFB call, and may release RRC connection from a LTE network 103 by receiving a RRC connection release message from the LTE network 103. The UE/MS 101 may perform a CSFB call process after making a transition to a circuit switched network, such as a wideband code division multiple access (WCDMA) network 105. After terminating the CSFB call and releasing the RRC connection with the circuit switched network, the UE/MS 101 may receive redirection information (“redirection info”) to switch back to the LTE network 103. Hereinafter, the UE/MS 101 may be referred to as a terminal or a mobile terminal.
The LTE redirection information may be used for the switching back from the 3G wideband code division multiple access (WCDMA) network to a 4th generation (4G) LTE network.
However, few networks supporting a 3G RRC connection release message with LTE redirection information in a 3G network exist for various reasons. For example, if a packet switched session for a data communication exists, the redirection information is not sent until the PS session is terminated. Accordingly, suggestions have been made to develop a system architecture supporting a fast return to an LTE network from a 3G network to an LTE network without waiting for normal termination of a packet switched (PS) session.
However, in the fast return scheme, if a packet switched (PS) session is found in a process of closing sessions after processing a call, a terminal supporting the fast return to an LTE scheme may transmit a signaling connection release indication (SCRI) message to a network to close the corresponding PS session. After the PS session is closed, the terminal may execute a transition to an LTE network.
In the fast return scheme, however, the terminal may transmit the SCRI message to close an active PS session while waiting for a response for a routing area updating request, thereby the terminal may attempt a transition to the LTE network without receiving the response for the routing area updating request. In this instance, since a context of switching between RATs may not be successfully transferred, the location registration in an LTE network may fail and voice call and data communication failures may occur until a successful location registration in the LTE network.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form any part of the prior art nor what the prior art may suggest to a person of ordinary skill in the art.